The present invention relates to a method of continuously winding yarn on a bobbin or the like.
In continuously winding yarn on bobbins, which are driven with the same circumferential speed, one distinguishes three different methods: scrambled winding, precision winding and stepwise precision winding.
In scrambled or pie winding the yarn guide reciprocation frequency is constant. Hence a constant yarn deposit angle results. Since however the rotation speed decreases with increasing bobbin diameter, the winding number i, i.e. the ratio of rotation speed to changing frequency, decreases with increasing diameter. When the winding number is a whole number or takes a value which differs from a whole number by a simple fraction, e.g. 11/2 (2 order), 22/3 (3. order), 53/4 (4 order), the so-called "mirror winding" results. For the sake of brevity in the following the numbers, for which mirror winding arises, i.e. the whole and fractional numbers, are designated as "mirror values".
The characteristic feature of a mirror winding is that the mirror winding is exactly laid on an already previously laid winding.
With integral winding numbers, i.e. with mirror values of the first order, the windings are put down in lays following each other. It is generally true that with a mirror value of the Mth order the winding of the K+M th lay is deposited exactly on the winding of the Kth lay.
A "lay" is defined as the yarn piece, which is laid on the bobbin during a twin stroke, i.e. while the yarn changing guide moves from one end of the bobbin to the other and back. A "winding" is defined as the yarn piece, which is laid during a revolution. The winding number i is the number of windings per lay.
Mirror windings can cause a series of difficulties, particularly unstable bobbin structures, difficulties in take-off on the concerned bobbin and nonuniformities in a subsequent dyeing process.
In high precision winding the yarn guide reciprocation frequency keeps a fixed relationship to the rotation speed of the bobbin; the winding speed also remains constant. Accordingly the bobbin rotation speed, and also the yarn guide reciprocation frequency, is always smaller with increasing bobbin diameter. The consequence of this is that the yarn deposit angle is always smaller. It is approximately proportional to the yarn guide reciprocation frequency. The consistency of the yarn wound on the bobbin deteriorates with smaller deposit angle. This method has only limited usefulness. It does however have the advantage that one can avoid mirror structure by proper selection of the winding number.
In stepwise high precision winding the wind up occurs in several steps. In each individual step the yarn guide reciprocation frequency f decreases in proportion to the bobbin rotation speed n. The winding number i=remains constant in each step. It is selected in a known method so that at the beginning of each step the maximum allowed yarn guide reciprocation frequency is used, i.e. the maximum deposit angle, which is approximately proportional to the winding number for a given diameter, is used in the method. The transition to the next step occurs in the known method normally when the deposit angle has reached the smallest allowed value. On transition to the new step the changing frequency is increased discontinuously so that the maximum yarn guide reciprocation frequency and the maximum deposit angle again adjust themselves as above. Accordingly the winding number jumps to a new smaller value. Thus the winding number can decrease by chance to a mirror value or into its critical range.
According to the Published German Patent Application 40 37 278, on which the invention is based, a computer determines from step to step the winding number and compares it with the approximate mirror value. When the calculated winding number does not fall in the critical region of the mirror value, it is used in operation. When it is in the critical range of the mirror value, a slightly larger winding number is used. This winding number is within a certain definite short distance from the mirror value, which depends particularly on the size and order number of the mirror value. Because of that, the winding of the (K+M)th lay is not deposited exactly on the winding of the Kth lay, but is displaced a predetermined lay spacing a from the winding of the Kth lay. The lay spacing a is determined from yarn center to yarn center and is thus necessarily larger than the width of the deposited yarn. It is recommended to make it as small as possible, if possible not larger than twice the width of the yarn.
According to the above-mentioned reference one tries to keep the number of the correct engagement as small as possible. Thus in that step the winding proceeds only with the correct winding number, in which a mirror winding is avoided. In the other steps one uses winding numbers, which result when one selects the maximum allowed changing frequency as the starting frequency. With this winding number the spacing of the windings of the corresponding lays are determined by chance and thus are nonuniform.